It is well known that many chemical reactions are exothermic, i.e. they produce heat, and examples of such reactions include acid-base reactions
The present invention makes use of a controlled exothermic reaction to produce heat which is then exchanged in a heat exchanger to provide a usable source of heat for heating a fluid such as the water in a domestic water supply
Accordingly, in a first aspect, the invention provides a method for producing a supply of a heated fluid, which method comprises passing the fluid through a heat exchanger unit where it is heated by a heat source; characterised in that the heat source derives heat from the exothermic reaction of two or more chemical reactants
The exothermic reaction may take place inside a reactor within the heat exchanger. Alternatively, the reactants may be mixed together in a vessel that is separate from the heat exchanger unit, and a stream of the mixed reactants and/or their reaction products may be passed through the heat exchanger to serve as the heat source
In one embodiment, the invention provides a method for producing a supply of a heated fluid, which method comprises passing the fluid through a heat exchanger unit, wherein the heat exchanger unit comprises:
(a) a heat exchanger element through which the fluid may flow;
(b) a reaction chamber having at least one inlet through which reactants may be introduced into the reaction chamber, and at least one outlet through which spent reactant may be removed from the reaction chamber;
(c) a first dosing unit for introducing a controlled amount of a first reactant through an inlet into the reaction chamber; and
(d) a second dosing unit for introducing a controlled amount of a second reactant through an inlet into the reaction chamber;
wherein the first and second reactants react exothermically and the heat thereby produced is exchanged with the fluid passing through the heat exchanger element, the introduction of the first and second reactants into the reaction chamber being controlled to produce a required level of heating.
The fluid can be a gas or a liquid.
In one embodiment, the fluid is a gas.
In another embodiment, the fluid is a liquid, one particular example of which is water.
The heat exchanger element is in thermal contact with the reaction chamber. In one embodiment, the heat exchanger element passes through the reaction chamber. For example, the heat exchanger element can take the form of a pipe passing through the reaction chamber.
It will be appreciated that the fluid does not come into contact with the reactants.
The reaction chamber has at least one inlet and at least one outlet. Each reactant may be provided with its own inlet. Alternatively, a pre-mixing chamber may be provided into which the first and second reactants are introduced prior to introducing them into the reaction chamber. It is preferred, however, that each reactant has its own inlet.
Dosing units are provided for introducing the first and second reactants into the reaction chamber in a controlled manner so as to produce a required level of heating. Each dosing unit can take the form of a container (e.g. a hopper or a tank) having an aperture that may be opened or closed to permit a reactant to move towards the reaction chamber. The or each reactant can be conveyed to the reaction chamber by means of a gravity feed. Alternatively or additionally, a pump or other conveying device (e.g. an auger or screw) may be used.
One or more sensors may be provided for measuring the temperature of the fluid when it exits the heat exchanger. The sensors are typically connected to a controller which may in turn be connected to the dosing units and/or a valve at each inlet into the reaction chamber. Sensors may also be provided for monitoring the rate of flow of reactants into the reaction chamber.
One or more reaction monitoring sensors may also be provided for monitoring the extent of reaction between the reactants. A reaction monitoring sensor (which may be for example a pH sensor) may be disposed in the vicinity of, or at, the or each outlet to determine whether or not the reaction between the reactants has been completed. The reaction monitoring sensor may be linked to the controller and/or directly to a valve or other closure device closing each outlet. The valve or other closure device may be actuated to an open position in response to a signal from the reaction monitoring sensor or the controller to allow spent reactant to exit the reaction chamber.
In each of the foregoing aspects and embodiments of the invention, the reactants (e.g. the first and second reactants) are preferably an acid and a base respectively.
The acid and base are preferably selected and/or formulated so as to provide an extended reaction time thereby giving a more prolonged release of heat.
Particular examples of acids are those having a pKa value of >0, more typically >2 and preferably >3, e.g. a pKa in the range 3 to 7. Where the acid is polybasic (e.g. citric acid), the foregoing limits refer to the first ionisation).
Particular acids are polybasic acids.
A preferred acid is citric acid.
Examples of bases are those having a pKb value of >0, more typically >2 and preferably >3, e.g. a pKb in the range 3 to 7.
Particular bases are basic amines and in particular mono-, di- and trialkylamines. The bases, particularly the more volatile amines such as ethylamine (boiling point 16.6° C.) may be provided in the form of an aqueous solution or a gel.
One group of preferred bases consists of mono-, di- and trialkylamines in which each alkyl group contains from 1 to 4 carbon atoms, more preferably 1 to 3 carbon atoms and most preferably 1 or 2 carbon atoms. Such bases include methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine and triethylamine. Other bases that may be used include alkali metal hydroxides such as sodium hydroxide (caustic soda) and carbonates such as sodium carbonate
A particularly preferred base is ethylamine, for example in the form of a 50-70% aqueous solution or gel.
The acid and base and/or their physical form are selected so that when they are mixed (e.g. introduced into the reaction chamber), they provide a sustained release of heat rather than a rapid sudden increase in temperature followed by a similarly rapid fall in temperature. The sustained release of heat may be achieved by using relatively weak acids or bases that react relatively slowly. Alternatively, or additionally, the acid and/or the base may be formulated and/or presented in a physical form whereby reaction between them is slowed down. For example, depending on the natural physical state of the acid and the base, they may be introduced in the form of coated particles (e.g. coated powders or granules) or gels in which the coatings or gel components slow down the reaction between the acid and bases.
In one embodiment, the base may be in liquid or gel form and the acid may be in solid form. One such combination of acid and base is the combination of citric acid in solid form and aqueous ethylamine.
In another embodiment, the base is in solid form and the acid is in liquid form.
The reaction between the acid and the base may be carried out in the absence of water or in the presence of water. In one embodiment, no water is added to the reaction mixture.
In one preferred mode of operation, where a reaction chamber forms part of the heat exchanger, metered amounts of the first and second reactants are introduced into reaction chamber and the temperature of the fluid (e.g. water) emerging from the heat exchanger is monitored, further metered amounts of the first and/or second reactants being introduced once the temperature of the fluid falls below a predetermined FIGURE.
In a further aspect, the invention provides a heat exchanger unit for heating a fluid, the heat exchanger unit comprising:
(a) a heat exchanger element through which the fluid may flow;
(b) a reaction chamber having at least one inlet through which reactants may be introduced into the reaction chamber, and at least one outlet through which spent reactant may be removed from the reaction chamber;
(c) a first dosing unit for introducing a controlled amount of a first reactant through an inlet into the reaction chamber; and
(d) a second dosing unit for introducing a controlled amount of a second reactant through an inlet into the reaction chamber; and optionally
(e) one or more sensors for (i) monitoring a parameter indicative of the completeness of the reaction between the reactants; and/or (ii) the temperature of the fluid and/or (iii) the rate of flow of reactants into the reaction chamber; and
(f) a controller operatively linked to the one or more sensors for controlling flow of reactants into the chamber and flow of spent reactant out of the chamber.
The invention will now be illustrated in more detail (but not limited) by reference to the specific embodiment shown in the accompanying drawing.